Carbon and carbon-containing nanotubes are unique carbon-based, molecular structures that exhibit interesting and useful electrical properties. There are two general types of carbon nanotubes, referred to as multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs). SWNTs have a cylindrical sheet-like, one-atom-thick shell of hexagonally-arranged carbon atoms, and MWNTs are typically composed of multiple coaxial cylinders of ever-increasing diameter about a common axis. Thus, SWNTs can be considered to be the structure underlying MWNTs and also carbon nanotube ropes, which are uniquely-arranged arrays of SWNTs.
SWNTs are ideal quantum systems for exploring basic science in one-dimension. These novel molecular-scale SWNTs, derived by bottom-up chemical synthesis approaches, are also promising as core components or interconnecting wires for electronics and other applications. Rich quantum phenomena have been revealed with SWNTs and functional electronic devices such as transistors, chemical sensors and memory devices have been built. From both fundamental and practical points of views, it is useful to assemble nanotubes into ordered structures on large surfaces for addressable and integrated devices. Not only is it desirable to place nanotubes at specific locations with desired orientations, it is also desirable to scale such methods to large areas for the large-scale manufacture of nanotubes.
Patterned growth of carbon nanotubes (e.g., by chemical vapor deposition (CVD)) represents an assembly approach for placing and orienting nanotubes at a stage as early as the synthesis stage of the nanotube growth. Catalyst patterning on a substrate can be used to define the locations from which nanotubes originate, with van der Waals forces and/or influences determining the orientation of the nanotubes as they are grown. This approach has been successful in yielding nanotubes, including SWNTs, on small substrates for basic studies and device demonstrations; however, it is not necessarily applicable for surface catalytic patterning in large-scale implementations due to difficulties observed with nanotube growth. For instance, manufacturing difficulties can result in pyrolysis and/or low nanotube yield (e.g., low percentage of successful growth from catalyst growth sites). These and other factors have presented challenges to the large-scale production of carbon nanotubes, such as large arrays of nanotubes on full four-inch wafers.